In the production of polyurethanes, it is often desirable to control the activity of the catalyst(s). The effect of controlled catalysis may be realized in improved reactivity profiles, for instance, delayed initiation or accelerated cure. Such reaction rate control is of particular importance to the polyurethane molder, where it is important that the polyisocyanate/polyol mixture remain flowable for sufficient time to fill the mold properly, while maintaining or improving demold time. Controlled catalysis can also affect product distributions and significantly impact physical properties of the final polyurethane part.
Latent activity is generally achieved through the use of thermally activated "blocked" catalysts. An example is the ammonium salt prepared from a tertiary amine and a carboxylic acid (U.S. Pat. No. 3,862,150). The disadvantage of such a material is mainly corrosivity, but poor master batch stability has also been reported. A related structure is prepared from triethylenediamine and a glycol borate acid (U.S. Pat. No. 3,193,511; U.S. Pat. No. 3,127,404; FR 2,301,554). An ammonium salt of a quaternary borate results. The advantage of such a catalyst composition is delayed activity and/or accelerated cure. U.S. Pat. No. 5,086,081 describes reduced odor amine-boron compositions prepared from tertiary amine polyurethane catalysts and boric acid. These compositions also impart improved reactivity during the production of polyurethane parts. U.S. Pat. No. 4,542,214 describes the composition and synthesis of tertiary amine salts of substituted carbamic and carbonic acids, and their use as delayed action polyurethane catalysts.
Latent activity/accelerated cure has been noted for quaternary ammonium carboxylate salts prepared from triethylenediamine and ethylene oxide or propylene oxide in the presence of protic acid (U.S. Pat. No. 4,904,629; see also U.S. Pat. No. 4,040,992). Quaternary ammonium carboxylates are generally known to catalyze the trimerization of polyisocyanates (U.S. Pat. No. 4,503,226 and references cited therein).
Quaternary ammonium areneoxide zwitterions (U.S. Pat. No. 4,335,219) and sulfonium zwitterions (U.S. Pat. No. 4,111,914) have been used as catalysts for polyurethane reactions.
Quaternary ammonium carboxylate inner salts (zwitterions) have been prepared. The synthesis of (R)-carnitine (Tetrahedron Lett. 1992, 33, 1211-1212), betaine product from an anomalous Eschweiler-Clarke reaction (Tetrahedron Lett. 1991, 23, 3847-3848), and betaines derived from amino and hydrazino acids (Tetrahedron 1990, 46, 1911-1922) are examples.